Importing Existing Data
There are two ways to import existing data in to OpenCMS. The first, and more basic of the two, is to simply navigate to the folder in which you wish to put the content and click the "Upload" button in the upper left of the workplace. This will allow you to upload folders from your local disk.
The problem with this is that it doesn't allow you to set any advanced properties of the files you're importing such as which element of your templates these file represent. This is often good for small amounts of data in the simplest case.
If you need more control of the import, there is a Extended HTML Import tool in the Administrative -> Database Management section.